Variable condenser



April 15, 1930. v W. KELLOGG VARIABLE CONDENSER Filed Jan l5. 1927 2 Sheets-Sheet l www April 15, 1930. w. s. KELLOGG 1754,894

VARIABLE .CONDENSEB 2 sheets-shee .2

Filed Jan 15 y1927 mf??? t Patented Apr. .15, 1930 PATENT OFFICE WILLIAM S. KELLOGG, OF TEORIA, ILLINOIS VARIABLE CONDENSER Application led January 15, 1927. Serial No..161,273.

This invention relates to variable condensers, particularly such as are adapted to be used in radio frequency circuits of radio apparatus. The invention is fully described in the following specification and shown in the accompanying drawings, in which:

Fig. 1 isa top plan view of a condenser embodying the invention;

Fig. 2 is a vertical longitudinal section through the same 'on'tlie line 2--2 of Fig. 3; Fig. 3 is a front elevation of the device removed from a panel;

Fig. 4 is a front elevation-of the dial housing;

Fig. 5 is a sectional View through the dial housing on the line 5-5 of Fig. 4; and

Fig. 6 is a partial end elevation of the stator as viewed from the line 6-6 of Fig. 2.

The embodiment illust-rated comprises al condenser frame made up of front and rear plateslO and 11 having recesses 12 into which P are fitted spacer bars 13 of a suitable nonconductor such as hard fiber, rubber or some of the phenolic condensation products which are now commonly used for such purposes.

These are secured to the end plates 10 and 11 by means of screws 14 or the like.

A stator element A is secured between the spacer bars 13 by means .of'screws 15 and consists preferably of a casting having an internal screw thread which is adapted to receive the complementary screw threads of a rotor B which is mounted upon a shaft C and which is fed into and out of the the stator A by means of a screw D as the shaft C is turned and which is secured to the rear plate 11 by means of an extension 16 fastened through a hole- 17 in the plate, and a nut 18 screwed upon the threaded outer end of said extension.

The screw D has a hollow center 19 in which is journalled the reduced end 20 of the shaft C, the other being also reduced at 21 and journalled in the front plate 10. This shaft is turned by means of a knob E as shown in Fig. 5, as will be later explained. Y

The rotor B is made conical in form as is shown in dotted lines in Fig. 2 in its outermost position and in .full' lines in its innerthe stator A to the f ull depth.

most position. The screw threads of the rotor are thicker at the inside 22 than they are at the outside 23, while the internal threads of the stator are correspondingly shaped, being thicker at the outside 24 thanl they are at the inside 25 so that when the rotor B is turned to its full in position as shown in Fig. 2 in full lines, the rotor and stator are separated fromeach other by a small air gap which is preferably substantially uniform at all points throughout the screw threads. y

The rotor is turned by means of a longitudinal keyway 26 in the enlarged portion 27 of the shaft C and is engaged by a key 28 extending inwardly from the hubl 29 of the rotor B. This hub loosely surrounds the yscrew D but narrows at its inner end 30 and is provided with an internal thread 31 which engages the threaded member D. It willbe understood, of course, that the itch of the threads D is the same as the pitch of the threads of the rotor B. As the shaft C is turned it will act through the keyway 26 of the key 28 to turn the rotor B 75 and this will then be set in or out, depending upon which way the shaft C is turned., so as to move the rotor B into or outof the stator A.

The setting of the rotor B with respect to the stator A is accomplished by having the nut `18 loosened and turning the screw D until the rotor B can readily be turned into The screw D is then turned so as to bring the threads of the rotor B midway between the internal threads ofthe stator A, the outer edges 23 of the rotor threads being visible through the openings 32 in the shell or housing of the stator A. The nut 18 is then adjusted and the rotor can be fed into the stator by turning the shaft 21 since the pitch of the screw D is the same as the pitch of the screw threads Aof the rotor and the stator.

From the foregoing it will be apparent that due to the conical form' of the stator and rotor the capacity of the condenser is less as the thread of the rotor starts to enter the stator and builds up capacity 4more rapidly as the rotor nears its full-in position than out.

y It will alsov be apparent that this effect is vgreatly increased by making the threads -in-` clined so that they are thicker at their base and thinner at the edges. This tapering'of the threads causes the surfaces of the threads to approach each other as the rotor is screwed in While the conical form of the internaland external screws provides a means for increasing the overlapping of the threads as the rotor is screwed in, both of these acting to greatly increase the capacity of the condenser much more rapidly than would be the case where the screw thread was one of uniform diameter and each spiral of uniform-thickness throughout, in which case the capacity would vary in direct proportion to the length of the'thread engagement.

From the foregoing it will be clear that the capacity is dependent. upon three.- things; namely, the length of the threads in overlapping position, the ratio overlapping of these threads which varies due to the conical form and the distance between plates which varies due to the conical form and also to the wedge-shaped screw threads. This is of considerable advantage in a condenser for use in a radio frequency circuit for the reason that the rate of increase of capacity shall increase as the capacity itself increases.

Applicant preferably mounts his condenser upon a panel F by means of screws 33 as shown in Fig. 2. Figs. 4 and 5 show a preferred form of knob and dial which indicates the position of the rotor. The dial 34 has a hub 35 which is secured to the extension 2l by means of a set-screw 36. The hub 35 vis screw threaded to receive the knob E, the lower portion of the hub being turned and journalled in the dial housing 3,7 which is secured to the panel F by means of a screw 38. The shaft C and the housing 37 are preferably tensioned by means of a fiat spring 39 which is compressed by a nut 40 onthe screw threaded hub 35.

The outer edge of the dial 34 is. graduated as shown in Fig. 4, the graduation being ,readable through the window 4l in the housing 37. The dial 34 carries a pin 42 which operates the Geneva-gear 43 lwhich has a graduated dial 44 which has numbers indicating the number of threads of the screws which are in overlapping position. This 4dial is visible through the window 45 in the housing 37. Thus it will be seen that the dials 44 and 34 together show the exact position of the condenser elements. i

Stops are preferably used at the two ends of the movement of the rotor which engage the ends of the rotor thread but for sake of clearness, these are omitted.

While I have shown and described but a single embodiment of this invention, it is to be understood that it is capable of many m'odications. Changesl therefore in the construction and 'arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

l. A variable condenser comprising a coneshaped rotor rotatable about a central axis and having an exterior thread, a stator having a complementary hollow conical internally threaded space, and'means for feeding the rotor longitudinally of said axis whereby the threads are fed deeper radially intoveach other as the rotor is fed longitudinally into the stator, and means for insulating said rotor and stator from Ieach other.

2. A variable condenser comprising a coneshaped rotor rotatable about a central axis and having an exterior thread, a stator having a complementary hollow conical internally threaded space, and means for feeding the rotor longitudinally of said axis whereby the threads are fed deeper radially into each other the rotor is fed longitudinally into the stator, and means for insulatingsaid rotor and stator from cach other, said threads being thicker at the base than at the edge so as'to cause the threaded surfaces of the rotor and stator to approach each other as the rotor is screwed into the stator and vice versa. l

A variable condenser comprising a poneshaped rotor rotatable about a central axis and having an exterior thread, a stator-having a complementary hollow conical internally threaded space, means for feeding the rotor long itudinally of said axis whereby the other as the rotor is fed longitudinally into the stator, means for insulating said rotor and stator from each other, and means for indicating the number of turns the rotor is screwed into the stator.

4. A variable condenser comprising a coneshaped rotor rotatable about a central axis and having an exterior thread, a stator having a complementary hollow conical internally threaded space, means for feeding the rotor longitudinally of said axis, whereby the threads are fed deeper radially into each other as the rotor is fed longitudinally into the stator, means for'insulating said rotor and stator from each other, and a Genevagear for indicatingthe number of turns the rotor is screwed into the stator.

In testimony whereof I have hereunto affixed my signature.

WILLIAM S. KELLOGG.

threads are fed deeper radially into eachA 

